1. Field of the Invention
The present invention relates to an exhaust gas purifying method and an exhaust gas purifying apparatus of an internal combustion engine, and an exhaust gas collecting apparatus that can be used for the method and the apparatus.
2. Description of the Related Art
A catalytic converter that is used to purify the exhaust gas from an internal combustion engine has such characteristics that the catalytic converter cannot sufficiently exhibit its purification performance unless the catalytic converter is heated to a predetermined temperature range for activation. Therefore, various attempts are made to activate the catalytic converter rapidly. For example, the catalytic converter is disposed as close as possible to the exhaust port of the internal combustion engine. Alternatively, a delay control is carried out to intentionally delay the ignition timing at the time of cold start, thereby to try to rapidly activate the catalytic converter. However, when the catalytic converter is set close to the exhaust port, the catalytic converter is heated excessively after the warming up, and the catalytic converter is thermally degraded. In order to compensate for the reduction of the purification performance of the catalytic converter due to thermal degradation, it is effective to increase the holding quantity of a noble metal. In this case, the manufacturing cost of the catalytic converter increases. In the case of delaying the ignition timing, when the delay angle is made too large to obtain a maximum effect of temperature up, the combustion is aggravated, which aggravates the drivability. When the catalytic converter temperature-up speed is increased, the internal combustion engine discharges exhaust gas without purifying as it takes time from the starting of the warm-up till its completion.
Concerning the processing of the exhaust gas until the completion of the warm-up of the catalytic converter, Japanese Patent Application Laid-open No. 2002-70539 describes that it is possible to utilize an absorbent or the like for HC and utilize a zeolite catalyst for NOx. This publication also discloses that as a countermeasure against the emission of the trapped NOx from the catalytic converter by saturation of the zeolite catalyst, the exhaust gas passing through the catalytic converter is collected in a collection vessel such as a tank, and the collected exhaust gas is recirculated to an intake passage of the internal combustion engine in a similar manner to that of an exhaust gas recirculation (EGR) apparatus.
The apparatus described in Japanese Patent Application Laid-open No. 2002-70539 is based on the assumption that the zeolite catalyst traps NOx that is discharge data low temperature. The exhaust gas is collected only when the catalytic converter is substantially saturated and when the trapped NOx is discharged. When the zeolite catalyst is not yet saturated, the exhaust gas is not collected even if the catalytic converter is not sufficiently warmed up. For HC and CO, it is necessary to utilize means other than the zeolite catalyst, such as the HC absorbent, for example, to restrict the discharging of a HC and CO. Therefore, it is necessary to provide the absorbent of HC and CO, in addition to the zeolite catalyst and the collecting apparatus that collects the exhaust gas. Consequently, the structure of the exhaust gas purifying apparatus becomes complex, and it takes time and labor to manufacture and maintain the apparatus.